Industrial safety system (ISS) are often employed in industrial environments, such as oil and gas processing plants, to protect persons and the environment upon the occurrence of a dangerous event, such as a fire. For example, an ISS may be employed in a downstream petroleum processing plant, an upstream drilling site (e.g., an offshore or onshore drilling rig), or the like, to provide automatic shut-down of certain processes in the event of an emergency, such as a fire, a line rupture, processes variables exceeding operational limits, and/or the like. In the case of an emergency, it can be essential to close certain valves (e.g., to stop the flow of hydrocarbons to a process, to direct fluids in a certain direction, or the like), or to open certain valves (e.g., to drain away hydrocarbons, to release pressure, to direct fluids in a certain direction, or the like). The portion of the ISS responsible for enacting these types of process shutdowns is sometimes referred to as an emergency shutdown (ESD) system. An ESD system may be one of many components of an overall ISS used to prevent potentially dangerous events from escalating into dangerous situations. In plant environments, ESD systems often employ emergency shutdown (ESD) valves that can control the flow of fluids or gases (e.g., hydrocarbons) in response to the detection of a dangerous event. Such ESD valves can include fail-safe actuated valves that can be commanded to different states, and that automatically move into a fail-safe state (e.g., open or closed) in the event of an emergency.
There are three common fail-safe states; “fail-safe closed”, “fail-safe open”, “fail-safe steady”. In the case of fail-safe closed, if an ESD valve loses communication with a CLS, for example, it will move to or remain in (or “fail-safe” to) a closed position. Thus, the ESD valve is closed to prevent liquid or gas from passing through a pipe regulated by the ESD valve. In the case of fail-safe open, if an ESD valve loses communication with a CLS, for example, it will fail-safe to an open position. Thus, the ESD valve is opened to allow liquid or gas to pass (e.g., at maximum rate) through a pipe regulated by the ESD valve. In the case of fail-safe steady, if an ESD valve loses communication with a CLS, for example, it will remain steady, at the current state (e.g., remain as is). Thus, the ESD valve is maintained in its current portion (e.g., closed, opened, or partially opened) to continue to regulate flow in the same manner is has been.
In many instances, operation of ESD valves is controlled and coordinated by a central logic solver (CLS) of an ISS. A CLS can act as a central system coordinator that assesses current conditions, determines states for ESD valves based on the current conditions, and controls the ESD valves to operate in the determined states. For example, if a CLS receives information indicating that a hydrocarbon leak is occurring in a pipe regulated by a particular ESD valve, the CLS may determine that the ESD valve needs to be closed to stop the leak and command the ESD valve to close; thereby stopping the flow of hydrocarbons, and effectively stopping the leak. Once the source of the leak has been resolved, the ISS may return to normal operating conditions, and command the ESD valve to open; thereby allowing the flow of hydrocarbons and the related processes to resume.